The objectives of this project are to determine the influence of microwave radiation on cardiac tissue in vitro and in vivo. A method for exposing isolated rat atria to microwave radiation has been developed. Preliminary data suggested that 2.45 GHZ CW microwave radiation of 2 or 10 mW/g has no overt effect on the rate or force of contraction of isolated atria. Also, certain biochemical and physiological parameters, which are indicative of cardiac function, have been measured in unanesthetized rats during whole body ventral exposure to 2450 MHz CW microwaves. Preliminary data suggest microwave exposure of 10 mw/cm2 for 4 hr has no effect on heart rate, mean arterial blood pressure or colonic temperature.